The invention relates to a supported high efficiency catalyst for production of polyolefins and to the production of an improved support for these catalysts.
Organometallic compounds have been used in combination with transition metal compounds to catalyze the production of high molecular weight polymers from ethylene and alpha-olefins to produce polymers having high stereoregularity.
The basic catalysts used in these methods are formed by combining a transition metal salt with a metal alkyl or hydride. Titanium trichloride and an aluminum alkyl, such as triethyl aluminum or diethyl aluminum chloride, are often used. However, such catalysts generally have low productivity and produce polymer with low stereoregularity.
Isotactic polypropylene results from a head-to-tail linkage of the monomer units resulting in the asymmetric carbon atoms all having the same configuration. The isotactic index is one measure of the percentage of isotactic isomer in the polymer formed. Atactic polypropylene results from random linkage of the monomer units. Isotactic polypropylene is a highly useful commercial product having high tensile strength, hardness, stiffness, resilience, clarity and better surface luster. Polypropylene finds extensive commercial use in injection molding, film, sheeting, filament and fiber applications. Commercially useful polypropylene contains essentially the stereoregular or isotactic isomer.
For most applications, the polymer produced using these basic catalysts must be extracted to remove the atactic (non-stereoregular) polymer to increase the percentage of isotactic (stereoregular) polymer in the final product. It is also necessary to deash polymer produced by this method to remove access catalyst. The additional production steps of polymer extraction and polymer deashing add significantly to the cost of polymer produced with these basic catalysts.
The first improvement in these catalysts resulted from the use of mixed titanium trichloride and aluminum trichloride as the catalyst with an aluminum alkyl co-catalyst.
Later improvements centered on the supported catalysts. Many early supported catalysts were based on the reaction products of surface hydroxyl containing compounds with transition metal compounds. Examples include the reaction product of a transition metal compound with an hydroxy chloride of a bivalent metal, e.g., Mg(OH)Cl (British Pat. No. 1,024,336), with Mg(OH).sub.2 (Belgian Patents 726,832; 728,002; and 735,291), and with SiO.sub.2, Al.sub.2 O.sub.3, ZrO.sub.2, TiO.sub.2, and MgO (British Pat. Nos. 969,761; 969,767; 916,132; and 1,038,882).
Some later supported catalysts were based on the reaction products of magnesium alkoxides with transition metal compounds. Examples include the reaction product of a transition metal compound with Mg(OR).sub.2 (U.S. Pat. No. 3,644,318 and Belgian Pat. Nos. 737,778; 743,325; and 780,530.)
Other supported catalysts were based on the reaction products of magnesium chloride with transition metal compounds. Titanium compounds were reacted with MgCl.sub.2 (U.S. Pat. No. 3,642,746 and Belgian Pat. Nos. 755,185; 744,221; and 747,846).
Promoted catalysts result from the addition of certain Lewis bases (electron donors) to the catalyst system. The electron donor has in certain situations been combined with titanium trichloride during production of the catalyst. Electron donors have included the ethers, esters, amines, ketones and nitroaromatics. Although the promoted catalysts improved the isotactic index of the polymer, they generally still did not produce polymer of such quality and quantity as to permit the elimination of polymer extraction and polymer deashing to remove catalyst residue.
Recently, a catalyst component with sufficiently high yield to apparently eliminate the necessity for performing polymer deashing and polymer extraction was described in U.S. Pat. No. 4,149,990. However, this catalyst was produced in solution, requiring catalyst washing.